Jack Osbourne, 26, announced he has multiple sclerosis, an incurable autoimmune disease that attacks the central nervous system. He was diagnosed just two weeks after the birth of his daughter, Pearl Clementine.

Osbourne, who is the son of rocker couple Ozzy and Sharon Osbourne, toldPeople magazine: “I was just angry and frustrated and kept thinking, ‘Why now?’ I’ve got a family and that’s what’s supposed to be the most important thing.”

About 400,000 people in the U.S. are living with MS and about 200 people are diagnosed each week, according to the National Multiple Sclerosis Society. The disease causes the body’s immune system to attack myelin, the substance that sheaths the nerve fibers of the central nervous system. When any part of the myelin sheath or nerve fiber is damaged or destroyed, signals traveling to and from the brain and spinal cord are interrupted, which causes a variety of symptoms — from numbness in the limbs to paralysis or loss of vision.

The hallmark of MS is its unpredictability, with symptoms ranging from mild to severe and presenting differently in individual patients.

We spoke with Dr. Timothy Coetzee, chief research officer of the National Multiple Sclerosis Society, and Dr. Rosalind Kalb, vice president of the group’s Professional Resource Center, about Osbourne’s diagnosis, why the disease is so difficult to diagnose and predict, and what it means to be young with MS.

Coetzee: There’s no test a physician can do to find out if you’re at risk for MS. There’s no cholesterol test, no biomarkers. You diagnose by excluding other things in terms of neurological symptoms. For example, in Jack’s case, he had difficulty seeing. [Osbourne told People he was diagnosed after having lost 60% of his vision in his right eye.] If you were in a similar situation, your ophthalmologist will not directly say, ‘You have MS.’ You will be referred to a neurologist to see if something else is going on. Jack, for example, said he started experiencing tingling. All of these are indicators that something neurological is happening. The best way to lead to a confirmation is undergoing an MRI. They use a chemical to see if there is damage and white marks in certain areas of the brain. This combined with other symptoms leads to a diagnosis. Sometimes physicians will still wait another six months to see if things change. It’s a process, and we are trying to accelerate it.

What makes the disease so unpredictable and how does that affect patients?

Coetzee: In Jack’s case, he started experiencing visual problems, but it’s not certain what each person will experience. Everyone is different. The variation in symptoms reflects the different parts of the brain that are under attack. For some people, it’s the part of the brain that deals with movement and they have trouble walking, others have vision problems and others have very mild tingling. The brain is so complex and we don’t know what part the immune cells will attack. It’s unfortunately a question we don’t know the answer to at this point.

Kalb: You may have a reaction and then things go back to normal, or you may have to deal with things not going back to how they used to be, and you need to problem solve. Typically, after a diagnosis, people start thinking about what they have to do and who needs to know. What do they do about their work situation? It’s unpredictable. You spend your whole life putting together an image of yourself based on all the things that make you uniquely you. When a doctor says you have MS, it’s like another piece you need to fit into your picture and it’s hard to predict. When some people hear the news, they can lose it for a little bit, some people kind of close off and don’t want to believe it. Some learn to slowly deal with the information and see how it will fit into their lives and this can greatly help.

Most people are diagnosed with MS between the ages 20 to 50. Osbourne is young at 26. What’s the prognosis for someone with early-onset MS?

Coetzee: The good news is, someone young like Jack has a lot of options available in terms of treatment options. There are several disease-modifying therapies he can try. The focus of these are to alter the disease and to stop the immune system from attacking the brain, as well as altering where the immune system cells attack. There’s the phrase, ‘paying it forward’ and that’s essentially what they do. By stopping the attack, the brain and its functions are preserved for the future. We didn’t have this 20 years ago.

Jack is also said to be a very active young man, very energetic and fit. This will have a beneficial effect in the present and will also make a difference in the future. There are many therapies and approaches that can help movement symptoms.

Everyone is different, but most people like Jack who are diagnosed at a young age can lead very happy and productive lives. They may have some, but very little disability going forward. That’s what data tells us. Overall, individuals can look forward to happy futures even with this diagnosis. It’s a different world being diagnosed today than 30 years ago.

What’s the first step for someone recently diagnosed with MS? How can they move forward and be successful?

Coetzee: Maintain a strong relationship with your physician to help manage and monitor the disease. We can’t predict the future, but there are many treatment strategies. Be sure to take advantage of all the options and plan for the future by keeping these options open.

Kalb: People need to deal with the emotions that come with MS first. Some need to do this on their own or with family and friends. For other people, it’s helpful to sit down with a third party like a helpline or a therapist. It can help to think out loud and process those feelings. I want people to recognize that finding a professional to talk about their feelings with and laying out the next steps is a sign of strength, not a sign of weakness. People can help you get through this in the best possible way. You’re not alone.